In Vivo 3‐Dimensional Glenohumeral Joint Geometry Based Upon Magnetic Resonance Imaging and Computed Tomography Analysis Shows Deeper, Thicker, and Taller Glenoid Labrum Morphology at 12 O’Clock Position in Healthy Young Adults

Purpose To investigate location‐ and sex‐specific glenoid labrum morphology of healthy young adults in vivo, and the labrum's effects on depth and radius of curvature (ROC) of the glenohumeral joint. Methods Healthy young adults with no history of shoulder surgery, injury, or instability underwent computed tomography and magnetic resonance imaging scans. Bone, cartilage, and labrum tissues were segmented from the scans and used to create 3‐dimensional models for each participant. Measurements were made on the coregistered 3‐dimensional models. The labral thickness, height, and depth were expressed according to a clockface on the glenoid (3, 6, 9, and 12 o'clock locations). Glenoid depth and ROC were also measured. Comparisons were made between sexes and among clockface locations. Results Sixty shoulders of 30 individuals (15 males/15 females, average age: 25 ± 7 years, body mass Index: 25.4 kg/m 2 ) were included. Repeated segmentation of a subset of the data showed the average absolute differences in labrum depth ranged from 0.3 to 0.4 mm, the labrum thickness differences ranged from 0.3 to 0.8 mm, and the labrum height differences ranged from 0.4 to 0.8 mm between the original and resegmented scans. For the complete dataset, no location‐specific differences in labrum morphology were found between males and females. The 12 o'clock location was at least 5.0 mm deeper, 4.3 mm thicker, and 8.4 mm taller than any other clockface location (all P  < .001). The labrum increased the average depth of the glenoid between 2.4 and 5.6 mm in the anterior/posterior and superior/inferior locations, respectively ( P  < .001), contributing an average of 60.1% of the overall glenoid depth, and decreasing the average ROC by 22.6 mm in the anterior/posterior locations and by 8.8 mm in the superior/inferior locations. Conclusions The labrum in young healthy adults was found to be larger than previously reported in cadaver studies. The labrum at 12 o'clock is deeper, thicker, and taller than at other locations; however, no location‐specific differences were found between men and women. The labrum contributed significantly to the depth and created a more congruent joint by minimizing differences between humerus and glenoid ROC. Clinical Relevance Improved understanding of the morphology of the glenoid labrum in young adults may be used to guide surgical repair and design of anatomical shoulder replacements.